It is a correct assumption that extreme exercising can directly affect your menstrual cycle. This is especially true if the daily exercise is intense (3-4 hours per day) combined with a body weight that is below normal (BMI < 20). Excessively low body weight interferes with the functions of many hormones in your body halting ovulation. In addition, if your periods seem to come and go, this would be consistent with excessive exercise being the culprit. If this is your case, what you are experiencing is called exercise-induced secondary amenorrhea. This type of amenorrhea is a common and reversible disorder in female athletes. To cure it you simply need to reduce the intensity of your exercise regimen. However, please do keep in mind that there are other causes of light or absent periods. One common cause is hormonal birth control
pills that may trigger a hormonal imbalance. Mirena IUD is also known to affect the menstrual cycle. One of its side effects is having light or absent periods. A serious medical concern in many female athletes who over train is the experience of bone loss known as osteoporosis that is irreversible if amenorrhea persists long enough. I would recommend a visit to a primary care doctor
or gynecologist for more information.